| In order to improve the dimensional stability and mechanical properties of fast-growing Chinese fir wood and broaden its application scope,based on previous research results,this paper firstly treated wood with polyethylene glycol(PEG)to discuss the influence of its molecular weight and concentration on the dimensional stability and mechanical properties of wood.In order to improve the mechanical properties of wood caused by PEG treatment,the wood was treated with polyethylene glycol(PEG)and aluminum sulfate(AL)by vacuum pressure two-step impregnation,and the effect of sodium silicate concentration on the physical and mechanical properties of wood was compared with the two steps of sodium silicate and aluminum sulfate.On this basis,the effects of PEG molecular weight,concentration and concentration of sodium silicate on anti-swelling ratio,compressive strength along grain,bending strength and elastic modulus of bending were investigated by orthogonal test method,and the composite modification effect was evaluated by fuzzy mathematics method to optimize the ratio of polyethylene glycol/sodium silicate.Finally,scanning electron microscopy(SEM),Fourier Transform infrared spectrometer(FTIR),X-ray diffraction(XRD)and thermogravimetric analyzer(TG)were used to analyze the microstructure,surface functional groups,crystallinity and thermal stability of wood before and after modification.The main conclusions are as follows:(1)After PEG treatment,the water absorption of wood decreased and the dimensional stability was improved obviously.With the increase of PEG molecular weight from 600 to 2000,the weight gain rate,volume increase rate and water absorption rate of wood decreased gradually,while the water absorption volume expansion rate increased gradually but was lower than that of untreated wood.With the increase of PEG concentration,the weight gain rate and volume gain rate increased,water absorption rate decreased gradually and then tended to be flat,while the volume expansion rate decreased first and then increased slightly.PEG with molecular weight1000 at 20% concentration had the most obvious improvement on wood size stability,but PEG treatment had an adverse effect on wood mechanical properties.In particular,the flexural strength and flexural elastic modulus are reduced in different degrees.(2)The wood was treated by a two-step process containing 20%PEG1000,saturated aluminum sulfate solution and sodium silicate solution.Due to the swelling of cells by polyethylene glycol and the deposition of reaction products of aluminum sulfate and sodium silicate,the weight gain rate and volume increase rate were significantly increased by the synergy of the two.Compared with aluminum sulfate and sodium silicate treatment and PEG treatment alone,The compressive strength,flexural strength and flexural elastic modulus of wood along the grain are also improved.(3)The range analysis and variance analysis of PEG molecular weight,concentration and sodium silicate concentration show that the influence of each factor on the four indexes of anti-swelling ratio,compressive strength along the grain,bending strength and elastic modulus of bending are different,and the ratio combinations of each index are different when they are individually optimized.Therefore,the fuzzy comprehensive evaluation method is applied to comprehensively evaluate the four indexes,and the optimal ratio of PEG and sodium silicate is 1000 and 20%,respectively,and sodium silicate concentration is 25%.(4)SEM observation showed that PEG treatment attached to the cavity of wood cells and tracheid wall,and the reaction products of aluminum sulfate and sodium silicate were agglomerated and filled in the cell cavity.After PEG-aluminum sulfate/sodium silicate composite treatment,PEG made the distribution of reaction products in cells more uniform.In FTIR spectra of wood,the positions of the characteristic absorption peaks-oh and-Co did not change significantly,but the peak intensities were different.XRD analysis shows that the crystallinity of wood treated by the composite treatment is higher than that treated by PEG and aluminum sulfate/sodium silicate.TG test showed that the maximum pyrolysis temperature of the composite treated material was advanced,but the maximum pyrolysis rate was reduced,and the residual mass fraction of the untreated material increased from 3.99% to 31.62%,indicating a significant improvement in thermal stability. |
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